U.S. patent application number 10/510243 was filed with the patent office on 2005-08-25 for induction furnace.
This patent application is currently assigned to RUSTEC LIMITED. Invention is credited to Jeney, Peter.
Application Number | 20050185692 10/510243 |
Document ID | / |
Family ID | 9935004 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050185692 |
Kind Code |
A1 |
Jeney, Peter |
August 25, 2005 |
Induction furnace
Abstract
An induction furnace wherein a susceptor made from an alloy
comprising niobium, hafnium and titanium is positioned within the
induction coil of the furnace. Such a susceptor can withstand
prolonged use in an induction furnace, at high temperatures in the
presence of oxygen.
Inventors: |
Jeney, Peter; (Zug,
CH) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
|
Assignee: |
RUSTEC LIMITED
P.O. Box 3191, Romy HOuse, Kings Road Brentwood
Essex
GB
CM14 4FF
|
Family ID: |
9935004 |
Appl. No.: |
10/510243 |
Filed: |
April 11, 2005 |
PCT Filed: |
April 16, 2003 |
PCT NO: |
PCT/GB03/01649 |
Current U.S.
Class: |
373/157 |
Current CPC
Class: |
H05B 6/24 20130101; F27D
11/06 20130101 |
Class at
Publication: |
373/157 |
International
Class: |
H05B 006/22 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2002 |
GB |
0208792.2 |
Claims
1. An induction furnace wherein a susceptor made from an alloy
comprising niobium, hafnium and titanium is positioned within the
induction coil of the furnace.
2. An induction furnace as claimed in claim 1 wherein the alloy
susceptor is cylindrical in shape, the interior surface of the
cylinder forming the lining of the furnace chamber.
3. An induction furnace as claimed in claim 1 wherein the alloy
susceptor is cylindrical in shape and is embedded within a cylinder
of a refractory material, which forms the lining of the furnace
chamber.
4. An induction furnace as claimed in claim 3, wherein the
refractory material is a high purity alumina.
5. An induction furnace as claimed in claim 3 wherein the inner
surface of the cylinder of refractory material is formed with one
or more protrusions to assist progress through the furnace of the
material which is being heated by the furnace.
6. An induction furnace as claimed in claim 5 wherein the
protrusion or protrusions are in the form of one or more helical
flanges.
7. An induction furnace as claimed in claim 5 wherein the cylinder
is provided at each end with a rolling seal.
8. An induction furnace as claimed in claim 2 wherein means are
provided to rotate the cylinder about its major axis.
9. An induction furnace as claimed in claim 1 wherein the induction
coil is contained within a gas-tight chamber surrounding the
cylindrical wall of the furnace.
10. An induction furnace as claimed in claim 9 wherein means are
provided to fill the gas-tight chamber with nitrogen or inert
gas.
11. An induction furnace as claimed in claim 1 which is provided at
each end with an air lock.
12. An induction furnace as claimed in claim 1 which also comprises
means for precision injection of air, oxygen, water, steam or any
other oxidizer or reducing agents such as hydrogen, hydrogen
peroxide and hydrochloric acid into the furnace chamber.
13. An induction furnace as claimed in claim 1 comprising means for
temperature measurement at a plurality of locations within the
furnace chamber by detection and measurement of heat radiation from
said locations, for the purpose of furnace control.
14. An induction furnace as claimed in claim 1 wherein the alloy
susceptor further comprises zirconium.
15. An induction furnace as claimed in claim 14, wherein the alloy
susceptor consists of 88% niobium, 10% hafnium, 1% titanium and 1%
zirconium.
16. An induction furnace as claimed in claim 1 substantially as
herein before described with reference to and as illustrated in the
accompanying drawing.
17. Use of a furnace as claimed in claim 1 in the disposal of waste
materials, or roasting of ores or minerals.
Description
[0001] The present invention relates to an induction furnace and in
particular to an induction furnace which is particularly suitable
for the disposal of waste materials by high temperature thermal
oxidation, although it may be used in other applications, such as
for example roasting of ores and minerals.
[0002] Electrically powered furnaces in which heat is produced by
electrical induction are well-known. The basic structure of such
furnaces comprises an electrical coil within which is placed a
susceptor. Passage of alternating electrical current through the
coil produces heat in the susceptor which is used to heat the
furnace. A preferred material for the susceptor is graphite.
However, particularly at high temperatures, graphite is attacked by
oxygen and thereby eroded in use and therefore is unsuitable for
use in a furnace for prolonged use at high temperatures unless
oxygen is totally excluded from the furnace. Nevertheless, there
are applications of such furnaces where it is either not possible
to exclude oxygen or oxygen-releasing materials, or it is
advantageous in the application to use controlled amounts of oxygen
or other oxidizing materials. Attempts have been made to solve this
problem by chemical doping of the graphite or by using materials
other than graphite as the susceptor, but these have not been
entirely satisfactory.
[0003] It has also been known to use various refractory materials
for the purposes of heat insulation or heat shielding in induction
furnaces.
[0004] The present invention seeks to provide a susceptor made from
materials other than graphite which can withstand prolonged use in
an induction furnace, at high temperatures in the presence of
oxygen.
[0005] The present invention, accordingly provides an induction
furnace wherein an alloy susceptor comprising niobium, hafnium and
titanium is placed within an induction coil.
[0006] The present invention further provides the use of an
induction furnace wherein an alloy susceptor comprising niobium,
hafnium and titanium is placed within an induction coil in the
disposal of waste materials, or roasting of ores and minerals.
[0007] The susceptor material to be used in the present invention
is an alloy comprising niobium, hafnium and titanium alloy. In a
preferred embodiment the alloy can further comprise zirconium.
Preferably the alloy contains at least 70% niobium, 10 to 20%
hafnium, up to 5% titanium, for example at least 0.1%, preferably
at least 0.2% or 0.5% titanium, and 0 to 5% zirconium. In a further
preferred embodiment of the invention the niobium metal containing
alloy contains 10% hafnium, 1% titanium and 1% zirconium. A
particularly preferred type of niobium-hafnium-titanium alloy of
the present invention is that which is designated WC103 as supplied
by Wah Chang. The advantage of this material in combination with
induction coils lies in the fact that it has susceptor properties
almost as good as graphite and is light weight and resistant to
chemical influences. This chemical resistance does not require an
internal surface protection layer for most applications and the
alloys of this group are withstanding high stress levels at
elevated temperatures of over 2000.degree. C.
[0008] It is preferred that the susceptor is in the shape of a
cylinder which forms the wall of the furnace chamber. In a further
preferred embodiment of the present invention, the susceptor can be
embedded within a refractory material which forms the wall of the
furnace chamber.
[0009] The term "embedded" in the context of the present invention
refers to the inclusion of the alloy susceptor in the cylinder of
the refractory material by providing a corresponding slot in the
refractory material into which the alloy susceptor can be slid.
Once the alloy susceptor has been positioned, any remaining space
within the slot can be filled, for example, with a suitable
particulate material such as carbon black and the end of the
refractory cylinder through which the alloy susceptor has been
inserted can be blocked off, for example, by a cylindrical
extension to the corresponding end plate of the furnace which can
protrude into the cylindrical slot.
[0010] The refractory material to be used for chemically aggressive
materials in the present invention is preferably chemical
resistant, has high thermal shock resistance, a low coefficient of
thermal expansion and refractoriness at least up to 1700.degree. C.
High purity alumina is particularly suitable although it is
envisaged that other suitable materials such as advanced plasma
sprayed composites can be used. When high purity alumina is used it
is preferable that its purity is at least 99% and more preferable
at least 99.5%. Particularly preferred types of material for use in
the furnaces of the invention are those which are designated SKA
100 NG and Alsint 99.7 as supplied by the firm Haldenwanger.
However, other similar materials can be used.
[0011] It is possible to use two or more susceptors in series in an
induction furnace in which case each susceptor would be surrounded
by a corresponding coil. For maximum efficiency the induction coil
is about 11/2 times the length of the susceptor and the susceptor
is positioned symmetrically within the coil.
[0012] It is preferred that the coil, or coils, of the furnace are
contained within a gas-tight chamber surrounding the cylindrical
refractory wall of the furnace. This provides a safety factor in
the unlikely event, that the wall of the refractory material should
crack and release gases from the furnace chamber. In such an event
the gases would still be retained within the furnace by the
aforesaid gas-tight chamber which is preferably provided with means
to fill it with nitrogen or some other inert gas. It also provides
the ability to operate the furnace with an exactly dosed quantity
of oxidizer.
[0013] The furnace will preferably be arranged to operate at a
slight angle of from 1.degree. to 20.degree., preferably 5.degree.,
to the horizontal so that material fed through the furnace at its
upper end is assisted by gravity to move to the lower end. To
further assist the progress of the material through the furnace,
means are provided to rotate the cylinder about its major axis.
Furthermore, the inner surface of the cylinder is preferably formed
with one or more protrusions to assist progress through the furnace
of the material which is being heated by the furnace, such
protrusion or protrusions being preferably in the form of one or
more helical flanges.
[0014] Particularly in applications such as the disposal of waste,
but also in other possible applications of the furnace, it is
important that the furnace provides a sealed environment and to
this end rolling seals may be provided at each end of the cylinder,
such seals being made of suitable steel, and further that air locks
are provided also at each end of the furnace.
[0015] Regarding the use of refractory materials in the furnace, it
will be appreciated that the whole of the revolving part of the
furnace should be very adequately supported in order to prevent
undue stresses in the refractory material.
[0016] For such applications as waste disposal it is also desirable
to provide means for injecting air, oxygen, water, steam or other
oxidizers or reducing agents such as hydrogen, hydrogen peroxide
and hydrochloric acid, into the furnace chamber in order to control
the chemistry of hydrolysis between 600.degree. C. and 1000.degree.
C., preferably 950.degree. C. of the particular waste disposal
operation which is being performed.
[0017] With a view to controlling the furnace it is also desirable
to include means for temperature measurement at a plurality of
locations within the furnace chamber) by detecting and measuring
heat radiation from said locations.
[0018] The induction furnace of the invention will now be
illustrated by way of example with reference to the accompanying
drawing in which:
[0019] FIG. 1 is a vertical section of the main part of an
induction furnace in accord with the present invention; and
[0020] In the furnace exemplified, a cylinder of an alloy
comprising niobium, hafnium and titanium (1) having a length of
approximately 4 metres, an internal diameter of approximately 0.5
metre and an external diameter of approximately 0.52 metre, and is
held between two annular end plates (2, 3). The structure is
positioned at a slight angle to the horizontal so that the plate
(2) can be regarded as an upper end plate and plate (3) can be
regarded as the lower end plate. The cylinder is held in position
by two resistant rollers (4,5).
[0021] Surrounding cylinder (1) is an induction coil (6) having a
length of approximately 2 metres and a thickness of approximately
0.015 metres. The induction coil (6) is encased in a steel cover
(7) so that the system occupies a gas-tight space surrounding the
furnace chamber which can be filled with nitrogen or other inert
gases.
[0022] To assist the movement of material which is being
heat-treated through the furnace chamber (8), a helical protrusion
(9) is formed integrating with the internal surface of the
cylinder.
[0023] The whole structure is mounted at each end on bearings (not
shown) to provide rotation, and rolling seals and airlocks (also
not shown) are also fitted at both ends of the furnace. This
ancillary equipment, along with the electrical circuitry of the
induction heater and also the heat radiation detector means and
related control equipment are all of a conventional nature and
therefore need not be described in order to enable the skilled
person to operate the new furnace structure of the invention.
[0024] It will be understood that many variations could be adopted
based on the specific structure hereinbefore described without
departing from the scope of the invention as defined in the
following claims.
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